There are various types of touch panels such as resistance film touch panels, optical touch panels, static capacity touch panels, ultrasonic touch panels and electromagnetic inductive touch panels. Among all, resistance film touch panels are widely employed in these days mainly in mobile devices, since these touch panels have advantages of being less expensive and convenient in thinning and weight-saving and allowing external input merely by attaching on the display surface. With the remarkable progress in mobile devices such as cellular mobile telephones and personal digital assistants in recent years, it has been strongly required to achieve a high visibility under sunlight and develop thinner and lighter devices.
In a resistance film touch panel, a fixed substrate provided with a transparent conductive film and a movable substrate provided with a transparent conductive film a replaced in such a manner that the transparent conductive films face to each other via a space. By pressing the panel, the transparent conductive films are brought into contact with each other and the resistance at this point is detected, thereby detecting the contact site. A touch panel is usually attached to the surface of a display. In this case, there arises a problem that two air layers are formed and the visibility is seriously worsened due to the reflection at each air face. Moreover, there arises another problem that the device per se becomes thicker.
As a measure thereto, an inner touch panel having the function of a resistance film touch panel inserted between a polarizing plate and a liquid cell is proposed in JP-A-5-127822 and Gekkan Disupurei (1999.01, p. 69). According to this system wherein a circular polarizing plate comprising a polarizing plate combined with a retardation plate is placed outside (in the visible side) the touch panel from the liquid cell, the interfacial reflection in the touch panel is considerably lessened and the visibility is improved. In an inner touch panel, however, a cellulose ester film serving as a protective film for the polarizing plate is provided in the input side and, therefore, sufficient scuff resistance and visibility cannot be always achieved on the surface in the input side.
Moreover, a polarizing plate should be placed in such a manner as to incline the transmission axis of the polarizing plate by 45° in the lengthwise or crosswise direction of the screen of a liquid crystal display unit. Therefore, a polarizing plate produced in a roll form should be punched at 45° to the longer direction in the punching step. Subsequently, the thus punched polarizing plate should be bonded while controlling the axis angle to a retardation plate or the-like to a definite level, if necessary. In case of punching in the direction of 45°, the plate becomes unusable at the roll edges, which brings about another problem that the yield is lowered particularly in a large sized plate.
In producing a touch plate having a circular polarizing plate in the upper substrate, a touch panel electrode such as an silver electrode and/or an insulating coat are printed on the transparent conductive film in one side of the circular polarizing plate in the subsequent step. However, printing cannot be performed continuously since the circular polarizing plate has been already punched out in this case. Therefore, it is unavoidable to employ a sheet-fed printing procedure and thus there arise problems in productivity and cost.
As the circular polarizing plate, use is made of a retardation plate such as a λ/4 plate or a combination of retardation plates such as a λ/4 plate with a λ/2 plate. Since a polarizing film has a high moisture content, it has been a practice to bond a retardation film to a polarizing film via a protective film. As a result, the circular polarizing plate per se becomes thicker, which interferes the construction of thinner and lighter liquid crystal display units. In the case of an inner touch panel, moreover, a circular polarizing plate is used in the upper substrate of the touch panel which is the movable substrate. Therefore, the input load (hereinafter referred to as the ON load) is elevated with an increase in its thickness, which brings about another problem of worsening in the input touch.
To improve the visibility by preventing the reflection on the touch panel surface, there is proposed a method of forming an antireflective layer on the surface. By combining such an antireflective layer with an inner touch panel, in particular, both of the internal reflection and the external reflection can be lessened and thus the visibility can be remarkably improved. Because of having only an insufficient scuff resistance, however, an antireflective film is frequently damaged when used on the touch panel surface. Therefore, it is impossible at present to use an antireflective film on the touch panel surface.